Combinatorial electrochemical deposition and testing system

ABSTRACT

An electrochemical deposition and testing system consisting of individually addressable electrode arrays, a fully automated deposition head, and a parallel screening apparatus is described. The system is capable of synthesizing and screening millions of new compositions at an unprecedented rate.

[0001] This application is a continuation-in-part of U.S. patentapplication 08/941,170 filed Sep. 30, 1997, pending, the techniques ofwhich are incorporated herein by reference for all purposes

FIELD OF THE INVENTION

[0002] The present invention relates to methods and apparatus for theelectrodeposition of diverse materials. More specifically, the inventioncomprises a fully automated electrochemical deposition and testingsystem for the synthesis and parallel screening of distinct materials onarrays of individually addressable electrodes.

BACKGROUND OF THE INVENTION

[0003] Among the different techniques for the preparation of metaldeposits, electrodeposition (also known as electroplating) isparticularly attractive because of its relatively inexpensiveinstrumentation, low temperature operation, and simplicity. A furtheradvantage of the technique is the relatively straightforward control ofthe thickness and composition of the depositing layers throughelectrical quantities such as current passed and potential applied.

[0004] Electroplating has been employed in small scale as well asindustrial processes. For example, electroplating of precious metals toimprove the appearance of an article or to create special effects iswell known. Electroplating is also employed to improve the corrosionresistance of corrosive substances by depositing thin surface films ofcorrosion resistant metals such as zinc, tin, chromium, nickel andothers. Wear resistant and friction modifying coatings of nickel,chromium, titanium and other metals and their alloys are used to improvethe wear resistance of bearing surfaces. Electroplating is also employedin the electronics industry to improve or modify the electricalproperties of substrates such as contacts, printed circuits, electricalconductors, and other electrical items in which specific surface orsurface-to-substrate conductive properties are desired. Distinct metalsare often electroplated onto metal surfaces to improve solderingcharacteristics or to facilitate subsequent coating by painting orapplication of other adhering films such as plastics, adhesives, rubber,or other materials.

[0005] Although the electrodeposition of a single material has beenextensively studied, the deposition of two or more metals byelectrochemical methods is difficult because the conditions favorablefor the deposition of one metal may differ substantially with thosenecessary for the deposition of the other. Factors including widelydiffering reduction potentials, internal redox reactions that can alterthe oxidation states of the materials in solution, and species that areor become insoluble during the deposition can disrupt the process.Moreover, the nature of the electrodeposit itself is determined by manyfactors including the electrolyte composition, pH, temperature andagitation, the potential applied between the electrodes, and the currentdensity. These issues are more prevalent as the complexity of theelectrodeposit (and hence the number of species in solution) increases.

[0006] Complex electodeposited materials are desired in areas such ascatalysis where the composition of the electrodeposit is critical to itscatalytic activity. The discovery of new catalytic materials dependslargely on the ability to synthesize and analyze new compounds. Givenapproximately 100 elements in the periodic table that can be used tomake such catalysts, and the fact that ternary, quaternary and greatercompositions are desired, an incredibly large number of possiblecompositions is generated. Taking each of the previously notedelectrochemical issues into account for every possible electrodepositand designing a synthetic strategy that can effectively cover phasespace using traditional synthetic methodologies is a time consuming andlaborious practice. As such, there exists a need in the art for a moreefficient, economical, and systematic approach for the synthesis ofnovel materials and for the screening of such materials for usefulproperties. See, for example, copending U.S. patent application08/327,513 entitled “The Combinatorial Synthesis of Novel Materials”(published as WO 96/11878).

[0007] As an example of the utility of exploring phase space for moreeffective catalysts, one can consider the effect of changing thecomposition of the anode in a direct methanol fuel cell. A tremendousamount of research in this area has concentrated on exploring theactivity of surface modified binary, and to a much lesser extentternary, alloys of platinum in an attempt to both increase theefficiency of and reduce the amount of precious metals in the anode partof the fuel cell. Although electrodeposition was explored as a route tothe synthesis of anode materials (e.g., F. Richarz et al. SurfaceScience, 1995, 335, 361), only a few compositions were actuallyprepared, and these compositions were made using traditional singlepoint electrodeposition techniques. Such an approach becomes veryinefficient when exploring and optimizing new multi-component systems.Recently, Mallouk, et al. reported work on combinatorialelectrochemistry as a route to fuel cell anode materials (Science, 1998,280, 1735), but this technique did not employ electrodepositiontechniques.

[0008] The present invention provides a method to use electrodepositionto synthesize and evaluate large numbers of distinct materials inrelatively short periods of time, significantly reducing the timeconsuming and laborious processes normally associated with a novelmaterials discovery program.

SUMMARY OF THE INVENTION

[0009] This invention provides methods and apparatus forelectrochemically depositing distinct materials on arrays ofindividually addressable electrodes. The invention also provides a meansof testing the as deposited materials for specific properties ofinterest.

[0010] One embodiment of the invention includes the individuallyaddressable electrode arrays and their associated fabrication andprocessing steps.

[0011] Another embodiment of the invention includes an automateddeposition system comprising a solution delivery head and its associatedelectronics and robotics. The delivery head is capable of automaticallydispensing precise mixtures of plating solutions to predefined locationsabove the working electrodes on the individually addressable electrodearrays. The head contains a reference and counter electrode, and whiledelivering the plating solutions completes a circuit with a givenworking electrode on the array. Adjusting the potential applied to theworking electrode on the array results in the deposition of materialsfrom the delivered plating solutions.

[0012] Another embodiment of the invention includes an electrochemicaltesting system comprising an electrochemical cell, a multi-channelpotentiostat, and an electronic interface designed to couple theaddressable array to the potentiostat such that individual electrodes onthe array may be addressed, either serially or in parallel, for themeasurement of a specific material property under investigation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to better understand the present invention, referenceshould be made to the following detailed description taken inconjunction with the accompanying drawings wherein:

[0014]FIG. 1A illustrates an array of 64 individually addressableelectrodes made in accordance with the present invention;

[0015]FIG. 1B illustrates an array of 66 individually addressableelectrodes made in accordance with the present invention;

[0016]FIG. 2A is a flow chart diagram describing the processes involvedin fabricating individually addressable electrode arrays;

[0017]FIGS. 2A and 2B are examples of masks for array fabrication;

[0018]FIG. 3 is a sectional view of the electrochemical deposition head;

[0019]FIG. 4A is a sectional view of the electrochemical cell;

[0020]FIG. 4B is a sectional view of the cathode assembly associatedwith the electrochemical cell of FIG. 4A;

[0021]FIG. 4C is an exploded view of the anode assembly associated withthe electrochemical cell of FIG. 4A;

[0022]FIG. 4D is a sectional view of the PCB interface associated withthe anode assembly of FIG. 4C;

[0023]FIG. 4E is a circuit diagram showing the electrical connections inthe PCB interface of FIG. 4D; and

[0024]FIG. 5 is a graph illustrative of the relationship betweenelectrode composition and associated activity for an example systemsynthesized and measured using embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention comprises an electrochemical synthesis andtesting system consisting of a number of separate parts includingindividually addressable electrode arrays, a fully automated depositionhead, an electrochemical cell and its associated electronics, and amulti-channel potentiostat. These components provide a means forinvestigating complex multi-component systems, by giving a user theability to rapidly synthesize and evaluate large numbers of diversematerials in short periods of time.

[0026] The individually addressable electrode arrays 10 of the presentinvention are illustrated in FIGS. 1A and 1B. The arrays 10 consist ofeither sixty-four or sixty-six independent electrodes 12 (with areas ofbetween 1 and 2 mm²) that are fabricated on inert substrates 14. Arrayswith as little as 10 or as many as 100 electrodes may be made inaccordance with the methods provided in the present invention. Examplesubstrates include, but are not limited to, glass, quartz, sapphire,alumina, plastics, or thermally treated silicon. Other suitablesubstrate materials will be readily apparent to those of skill in theart. The individual electrodes 12 are located substantially in thecenter of the substrate 14, and are connected to contact pads 13 aroundthe periphery of the substrate with wires 16. The electrodes 12,associated wires 16, and contact pads 13 are fabricated from conductingmaterials (such as gold, silver, platinum, copper, or other commonlyused electrode materials). In a preferred embodiment of the presentinvention, the arrays are fabricated on standard 3″ thermally oxidizedsingle crystal silicon wafers, and the electrodes are gold with surfaceareas of about 1.26 mm².

[0027] Still referring to FIGS. 1A and 1B, a patterned insulating layer18 covers the wires 16 and an inner portion of the peripheral contactpads 13, but leaves the electrodes and the outer portion of theperipheral contact pads exposed (preferably approximately half of thecontract pad is covered with this insulating layer). Because of theinsulating layer 18, it is possible to connect a lead (e.g., analligator clip) to the outer portion of a given contact pad and addressits associated electrode while the array is immersed in solution,without having to worry about reactions that can occur on the wires orperipheral contact pads. The insulating layer may be, for example,glass, silica (SiO₂), alumina (Al₂O₃), magnesium oxide (MgO), siliconnitride (Si₃N₄), boron nitride (BN), yttrium oxide (Y₂O₃), titaniumdioxide (TiO₂), hardened photoresist, or other suitable material knownto be insulating in nature.

[0028] Once a suitable inert substrate is provided, photolithographictechniques can be applied to design and fabricate electrode arraypatterns on it. By applying a predetermined amount of photoresist to thesubstrate, photolyzing preselected regions of the photoresist, removingthose regions that have been photolyzed (e.g., by using an appropriatedeveloper), depositing one or more metals over the entire surface andremoving predetermined regions of these metals (e.g., by dissolving theunderlying photoresist), one can fabricate intricate patterns ofindividually addressable electrodes on the substrate.

[0029] The process by which the individually addressable electrodearrays of the present invention are fabricated is described withreference to the flow chart illustrated in FIG. 2A. Starting with acleaning step 22 that comprises washing the wafer in a suitable solvent(such as methanol or isopropanol) followed by baking in a plasmacleaning oven, a photoresist deposition step 24 in which a first layerof photoresist is applied to the wafer is then done. Although manydifferent types of photoresist can be used for the same effect, thepreferred type in the present invention is Shipley Microposit S-1813 (orequivalent). The photoresist is applied to the wafer using a standardspin coating system (commonly used and familiar to those skilled in theart) which is set to leave a final thickness of between 1 and 2 μm onthe wafer. The photoresist is then cured at a predetermined temperaturefor a predetermined time to condition the photoresist. In a preferredembodiment of the present invention, the curing temperature is between90° C. and 130° C. and the curing time is between 30 sec and 2 minutes.

[0030] A primary electrode mask 27, an example of which is shown in FIG.2B, (which is the negative of the electrode array pattern desired) isthen placed over the wafer that is then photolyzed on a mask alignersystem (commonly used and familiar to those skilled in the art). Afterexposure to ultraviolet (UV) light during the photolysis step 26,regions 29 on the wafer are then dissolved away using an appropriatedeveloping solution (e.g., Shipley Microposit MF-319 or equivalent). Thewafer is then placed in a physical vapor deposition (PVD) system where ametals are deposited during a metal deposition step 28. Example PVDsystems include: sputtering, electron beam evaporation and pulsed laserdeposition. The metals deposited by the appropriate PVD system consistof an adhesion layer (such as Cr, Ta, or W) followed by the desiredelectrode material (such as Au, Ag, Cu or Pt). The thicknesses of theselayers may vary substantially, but are typically 100-500 Å for theadhesion layer and 1000-5000 Å for the electrode layer. Following alift-off step 30 to remove the excess metals, a second layer ofphotoresist is then deposited on the wafer during a second photoresistdeposition step 32, cured as described above, and photolyzed through anisolation mask 35 during a second photolysis step 34. The aim of thissecond photolysis step is to expose only the regions of the electrodepads 36 and an outer contact ring 38, the exposed photoresist on whichis dissolved away after the photolysis step. A final annealing step 40at between 90° C. and 130° C. for between 1 minute and 10 (or more)minutes hardens the remaining photoresist into an effective insulatinglayer. Alternately, an insulating layer (such as glass, silica, alumina,magnesium oxide, silicon nitride, boron nitride, yttrium oxide ortitanium dioxide) may be deposited in place of the hardened photoresistby a suitable PVD technique after photolysis of the second photoresistlayer through an inverse isolation mask (the negative of the isolationmask 35 in FIG. 2C).

[0031] The arrays of the present invention consist of a plurality ofindividually addressable electrodes that are insulated from each other(by adequate spacing) and from the substrate (since they are fabricatedon an insulating substrate), and whose interconnects are insulated fromthe electrochemical testing solution (by the hardened photoresist orother suitable insulating material). The number of electrodes can varyaccording to a desired number, but typically the arrays consist of 10 ormore electrodes, 30 or more electrodes, and preferably more than 50electrodes. In the embodiments shown in FIG. 1A and FIG. 1B, more than60 electrodes are in a single array. Materials are deposited on each ofthe individually addressable electrodes. Thus, an array of individuallyaddressable materials is also a part of this invention, with the numberof materials equaling the number of addressable electrodes. Thematerials in the array may be the same or different, as described below.

[0032] The deposition of materials on the above described electrodearrays to make a library of an equal number of compositions isaccomplished by the electrodeposition of species from solution usingstandard electrochemical methods. The compositions may all be the same,or may be different from each other. In one embodiment of the presentinvention, the depositions are carried out by immersing the electrodearray in a standard electrochemical deposition chamber containing thearray, a platinum mesh counter electrode, and a reference electrode(e.g., Ag/AgCl). The chamber is filled with a plating solutioncontaining known amounts of source materials to be deposited. Byselecting a given electrode and applying a predetermined potential for apredetermined amount of time, a particular composition of materials(which may or may not correspond to the exact composition of the platingsolution) is deposited on the electrode surface. Variations in thecompositions deposited may be obtained either by directly changing thesolution composition for each deposition or by using differentelectrochemical deposition techniques, or both. Examples of how one maychange the electrode composition by changing the deposition techniquecan include: changing the deposition potential, changing the length ofthe deposition time, varying the counter anions, using differentconcentrations of each species, and even using different electrochemicaldeposition programs (e.g., potentiostatic oxidation/reduction,galvanostatic oxidation/reduction, potential square-wave voltammetry,potential stair-step voltammetry, etc.). Through repeated depositionsteps, a variety of materials may be serially deposited on the array forthe aforementioned library.

[0033] In an alternate embodiment of the present invention, thedeposition of materials on the electrode array is carried out using apartially or fully automated solution delivery/electroplating systemconsisting of a deposition head and its associated syringe pumps,robotics and electronics. As illustrated in FIG. 3, the deposition head50 consists of a rod 52 that is tapered at the tip. The tapered end ofthe deposition head is wrapped with a mesh counter electrode 54 (e.g.,Pt) that is connected to an external power supply (not shown) via a wire56 that is embedded in the wall of the head. In a preferred embodimentof the present invention, the deposition head has a 1-3 mm ID which istapered to ca. 1 mm ID at the tip. A solution delivery tube 58containing an interannular reference electrode 60 is located into thecenter of the rod 52. The reference electrode 60 may be a standardreference electrode (such as Ag/AgCl, SHE, SCE or Hg/HgSO₄) or aquasi-reference electrode (such as a piece of Pt wire). The referenceelectrode 60 is split off from the solution delivery tube 58 andconnected to an external power supply or potentiostat (not shown). Theflow of liquids through the solution delivery tube 58 is controlled bycommercially available syringe pumps (not shown) that can preciselydeliver volumes of liquids with accurate displacements in the μL/hourregime. Although any number of syringe pumps can be used, at least oneis desirable and the exact number of pumps will ultimately depend on thecomplexity of the desired depositions (i.e., binary=two pumps,ternary=three pumps, quaternary=four pumps, etc.). The liquids that aredispensed from the aforementioned pumps are either mixed prior toentering the solution delivery tube (via an external mixer) or via afrit 62 embedded in the deposition head. During the deposition process,the deposition head 50 is held over a given electrode pad 12 on anelectrode array 10 by a clamp 68 that is connected to robotics (notshown) that can control its precise position. In a preferred embodimentof the present invention, the ideal position, as illustrated in FIG. 3,is ca. 1-2 mm above the electrode pad 12.

[0034] Still referring to FIG. 3, the operation of the automateddeposition system is described as follows. After positioning thedeposition head above a given electrode (sometimes referred to as the‘working’ electrode), the syringe pumps are activated causing apredetermined mixture of liquids containing predetermined amounts ofsource materials to flow through the tube 58 at an exactly specifiedflow rate and collect in a region 70 surrounding a given electrode 12.When the liquid contacts all three electrodes, a complete electriccircuit is formed in this region. Coincident with the formation of thiscircuit, a predetermined potential is applied to the working electrode(via an external power supply or potentiostat) causing species presentin the liquid above it to deposit on the electrode surface. After apredetermined deposition time, the head is rinsed and moved to the nextelectrode where the next specified mixture is delivered and plated out.In a preferred embodiment of the present invention, a deposition time ofbetween 1 and 2 minutes is used. The entire procedure can take less than3 minutes per deposition or about three hours per library of sixty-fourto sixty-six elements.

[0035] The electrochemical cell used to measure properties of thematerials deposited on the above described electrode arrays isillustrated in FIGS. 4A-4E. Referring to FIGS. 4A-4B, the cell 80comprises a cylindrical glass housing 82 (of approximate diameter equalto that of the wafers) that is sandwiched between two plastic endmembers 84. The anode array assembly 86, which holds the individuallyaddressable electrode arrays 10, is fit into one side of the cell, andthe cathode assembly 95, which holds a counter electrode 88 and itsassociated external wire coupling 96, is fit into the other side. Thecell is held together by four screw fasteners 90 which fit through holes98 located on the corners of the end members 84. A reference electrodecompartment 92 is bored into the glass housing to allow the insertion ofa reference electrode (not shown). A liquid filling hole 94 allows forthe filling and drainage of testing solutions from the electrochemicalcell.

[0036] Referring to FIG. 4C, an exploded view of the components of theanode assembly is shown. The glass housing 82 of the cell is fit overthe inner flange 106 of a molded adapter 102 and is held in placeagainst the adapter with an o-ring 100. This o-ring provides awater-tight seal for this part of the assembly. The diameter of theouter flange 104 of the adapter 102 is the same as that of the glasshousing, while that of the inner flange 106 is slightly smaller allowingone half of it to fit into the glass housing and the other half of it tofit into the remaining pieces of the anode assembly. A groove 108 is cutinto the lower lip of the adapter 102. This groove holds an o-ring 110which makes a water-tight seal with the anode array 10 when the adapteris pressed against it. Electrical contact to the anode array 10 is madeusing a ring of elastomeric contacts 114 which are pressed between theperipheral pads of the array (see FIGS. 1A-1B) and contact pads 122 on aprinted circuit board (PCB) assembly 112. These elastomeric contactscontain miniature wires encased in a flexible rubber sheath. They arecommercially available and known to those skilled in the art. The anodearray 10 is affixed to a backing plate 116 and attached to the PCB 112with screws (not shown) through holes 118. This backing plate holds theelectrode array and ensures contact between the peripheral pads on thewafer and the contacts on the PCB. This completes the anode assemblywhich is fitted together with screw fasteners 90 through holes 98 in endmember 84 as shown in FIG. 4A.

[0037] Referring now to FIGS. 4D-4E, the PCB 112 and its associatedcircuit diagram 130 are described as follows. The PCB 112 consists of arectangular plate 120 on which is deposited an intricate pattern ofwires and connectors. The contact pads 122, which provide electricalconnection to peripheral pads on the anode array (FIGS. 1A-1B), arerouted to four high-density pin connectors 128 that provide a cableconnection to an external power supply (not shown) or multi-channelpotentiostat 132. The multi-channel potentiostat 132 is essentially acollection of individual potentiostats bundled together in a singleunit. These individual potentiostats can precisely control the currentor potential applied to each electrode in the system. A common referenceelectrode contact 124 and a common counter electrode contact 126 arealso wired to the high density pin connectors so that individualelectrode pads on a given electrode array may be connected to the samereference and counter electrode during test measurements in theelectrochemical cell.

[0038] Using the PCB 112 in conjunction with the deposition head 50(FIG. 3) and the multi-channel potentiostat, each individual electrodeon a given anode array can be individually addressed (e.g., during anelectrodeposition procedure). Alternatively, using the PCB in connectionwith the electrochemical cell setup 80 (FIG. 4A) and multi-channelpotentiostat, all of the electrodes on the array my be simultaneouslyaddressed (e.g., during a catalytic activity measurement). Suchcatalytic measurements can be made in a time frame of between 1 and 2minutes for each array of materials.

[0039] In the PCB illustrated in FIG. 4D, a sixty-four contact padconfiguration is shown. It should be understood that a sixty-six contactpad configuration would be needed for experiments using a sixty-sixmember electrode array (FIG. 1B), and that PCB's having greater or lesscontact pads and associated connections are straightforward extensionsof the concept and intended to be included within the scope of thepresent invention.

EXAMPLE

[0040] The following example illustrates the electrochemical depositionand screening measurements for a very specific system using selectedembodiments of the present invention. It is only one of the manypossible uses of the present invention. The example illustrates how alibrary of sixty-four different Pt—Ru compositions may be prepared andtested for methanol oxidation activity. It should be understood that thesolution and electrode compositions, types of reference and counterelectrodes, applied and measured potentials, screening test conditions,and associated results are merely illustrative and that a person skilledin the art may make reasonable substitutions or modifications to thesecomponents without deviating from the spirit and scope of the invention.

[0041] A binary Pt—Ru library containing sixty-four different Pt—Rucompositions was synthesized on a sixty-four element individuallyaddressable electrode array (gold electrodes) using the electrochemicalreduction of acidic solutions containing mixtures of platinum chloride(H₂PtCl₆) and ruthenium chloride (RuCl₃). Starting with a stock solutionof 150 ml of 0.01M RuCl₃ (in 0.5M H₂SO₄) that was placed in a standardelectrochemical deposition chamber along with the electrode array, a Ptmesh counter electrode, and a silver/silver chloride (Ag/AgCl) referenceelectrode, the first working electrode on the array was held at aconstant potential of −0.25V (vs Ag/AgCl) for two minutes under constantstirring. The electrode array was then rotated in the deposition chamberand the solution composition adjusted (by the removal of a 5 ml aliquotof the RuCl₃ solution and its replacement with a 5 ml aliquot of a 0.01MH₂PtCl₆ solution), where the next electrode was deposited at the samepotential and for the same amount of time. This procedure was continueduntil all sixty-four electrodes were deposited with Pt—Ru compositions,whose thickness averaged between 1000-2000

. Analysis (via X-ray fluorescence measurements) of the sixty-fourelectrodes showed a continuously varying gradient of Ru and Ptcompositions among the sixty-four electrodes on the array.

[0042] This Pt—Ru library was then screened for methanol oxidationactivity by placing it into the electrochemical cell (described earlier)which was filled with a solution of 1.0M methanol in 0.5M H₂SO₄ (astandard testing solution composition for studying the electrooxidationof methanol in fuel cells). The cell also contained a Hg/HgSO₄ referenceelectrode and a Pt mesh counter electrode. Chronoamperometrymeasurements (i.e., holding a given electrode at a given potential andmeasuring the current that passes as a function of time) were thenperformed on all of the electrodes in the library by pulsing eachindividual electrode to a potential of −0.125V (vs Hg/HgSO₄) and holdingit there for 1 minute while monitoring and recording the current thatpassed. The results of this experiment are depicted in FIG. 5.

[0043] Referring now to FIG. 5, a three-dimensional plot 140 ofelectrode composition 142 (expressed as mole fraction platinum) versuscurrent 144 (in amps per square centimeter) versus time 146 (in seconds)is displayed. Individual electrodes are represented by theircompositions along the x-axis, with their associated activitiesrepresented by their current values on the z-axis. The most activeelectrode compositions 150 are centered around a 50:50 Pt:Ru electrodecomposition which agrees with results reported in the literature (e.g.,D. Chu and S. Gilman, J. Electrochem. Soc. 1996, 143, 1685). Althoughthe results plotted in FIG. 5 correspond to a simple binary library ofPt—Ru compositions made by the serial deposition of Pt—Ru solutions in astandard deposition chamber and studied by serial chronoamperometrymeasurements made on a single channel potentiostat, the same depositionsand measurements could be made in parallel with a multi-potentiostatusing the deposition head and PCB interface of the present invention(FIGS. 3 and 4D). In fact, significantly more complicated librariesusing ternary, quaternary and greater compositions are possibly simplyby changing the composition of the initial plating solutions. Platingsolutions comprising one or more of the water soluble forms of thetransition elements (e.g., Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr,Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg) as wellas many main group elements (e.g., Al, Ga, Ge, In, Sn, Sb, Te, Tl, Pb,Bi) can be used with the present invention, and will give rise toenormous variations in library compositions which can in turn be studiedin an enormous variety of catalytic systems.

[0044] As should now be readily apparent, the present invention providesa far superior method of electrochemically depositing and screening theproperties of diverse materials. Using this invention, one canefficiently prepare libraries of varying elemental composition, and,since these libraries are prepared on individually addressable electrodearrays, one can also directly measure properties of these compositions.Using the present invention, it should be possible to synthesize andscreen millions of new compositions at an unprecedented rate.

[0045] It is to be understood that the above description is intended tobe illustrative and not restrictive. Many embodiments will be apparentto those of skill in the art upon reading the above description. Thescope of the invention should, therefore, be determined not withreference to the above description, but should instead be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled. The disclosures of allarticles and references, including patent applications and publications,are incorporated herein by reference for all purposes.

What is claimed is:
 1. A method of fabricating individually addressableelectrode arrays, said method including the steps of: providing an inertsubstrate; applying photoresist to said substrate; photolyzingpreselected regions of said photoresist, said photolyzed regions beingremovable using a developer; depositing one or more metals on saidsubstrate; removing predetermined regions of said metals, the remainingregions forming said array of individually addressable electrodes. 2.The method of claim 1, wherein said step of photolyzing preselectedregions of said photoresist includes the steps of: placing an electrodemask over said wafer; and exposing said wafer to ultraviolet light. 3.The method of claim 1, wherein said step of depositing one or moremetals on said substrate comprises the deposition of an adhesion layerfollowed by the deposition of an electrode layer.
 4. The method of claim3, wherein said deposition of said adhesion layer comprises depositingbetween about 100 and 500

of a metal selected from the group consisting of Cr, Ta and W.
 5. Themethod of claim 3, wherein said deposition of said electrode layercomprises depositing between about 1000 and 5000

of a metal selected from the group consisting of Au, Ag, Cu and Pt. 6.The method of claim 1, further comprising the step of depositing aninsulating coating on selected regions of said substrate.
 7. The methodof claim 6, wherein said step of depositing said insulating coating onselected regions of said substrate includes the steps of: applying asecond layer of photoresist to said inert substrate; photolyzingpreselected regions of said photoresist, the remaining regions beingremovable using a developer; and annealing said substrate for apredetermined time at a predetermined temperature.
 8. The method ofclaim 7, wherein said step of photolyzing preselected regions of saidphotoresist includes the steps of: placing an isolation mask over saidwafer; and exposing said wafer to ultraviolet light.
 9. The method ofclaim 7, wherein said step of annealing said substrate comprises heatingsaid substrate at between about 90-130° C. for between about 1-10minutes.
 10. An array of individually addressable electrodes on an inertsubstrate, said array consisting of: a plurality of electrode pads; aplurality of contact pads; wires connecting said contact pads to saidelectrode pads; and an insulating layer covering said wires and apredetermined portion of said contact pads.
 11. The array of claim 10,wherein said electrode pads are located substantially in the center ofsaid substrate and said contact pads are located around the peripheraledge of said substrate.
 12. The array of claim 10, wherein said inertsubstrate is selected from the group consisting of glass, quartz,sapphire, alumina, plastic and thermally treated silicon.
 13. The arrayof claim 10, wherein said insulating layer is selected from the groupconsisting of glass, silica, alumina, magnesium oxide, silicon nitride,boron nitride, yttrium oxide, titanium dioxide, and hardenedphotoresist.
 14. The array of claim 10, wherein said electrode pads,said contact pads, and said wires are fabricated from conductingmaterials.
 15. The array of claim 14, wherein said conducting materialsare independently selected from the group consisting of gold, platinum,silver and copper.
 16. The array of claim 10, wherein said plurality ofelectrode pads comprises at least 10 electrodes.
 17. The array of claim16, wherein said plurality of electrode pads comprises up to 100electrodes.
 18. The array of claim 10, wherein said electrode pads havea surface area of between 1 and 2 mm₂.
 19. A method of depositingdiverse materials on individually addressable electrode arrays, saidmethod including the steps of: providing an array of individuallyaddressable electrodes, a power source, a reference electrode and acounter electrode; delivering a mixture of source materials topredetermined locations on said array; and depositing a predeterminedcomposition of said source materials on a given electrode on said array.20. The method of claim 19, wherein said step of delivering said mixtureof said source materials includes the steps of: positioning a depositionhead over a given electrode on said array; and activating apredetermined number of syringe pumps associated with said depositionhead, said activation delivering a predetermined composition of saidsource materials to said predetermined locations on said array.
 21. Themethod of claim 20, wherein said step of positioning said depositionhead over said given electrode is accomplished using robotics.
 22. Themethod of claim 21, wherein said robotics position said deposition headat a predetermined distance above said given electrode.
 23. The methodof claim 19 wherein said depositing step includes a step selected fromthe group consisting of changing the deposition potential, changing thelength of the deposition time, varying the counter anions, usingdifferent concentrations of said source materials, and selecting theappropriate electrochemical deposition program.
 24. The method of claim23, wherein said electrochemical deposition program is selected from thegroup consisting of potentiostatic reduction, potentiostatic oxidation,galvanostatic reduction, galvanostatic oxidation, potential square-wavevoltammetry, and potential stair-step voltammetry.
 25. An apparatus fordepositing diverse materials onto an array of individually addressableelectrodes, said apparatus comprising: a rod having a tapered end; asolution delivery tube within said rod; a reference electrode withinsaid solution delivery tube; a counter electrode attached to said rod;means for controlling the composition and flow rate of liquids throughsaid solution delivery tube; means for mixing said liquids before saidliquids exit said solution delivery tube; and means for controlling theposition of said apparatus over said array.
 26. The apparatus of claim25, wherein said means for controlling the composition and flow rate ofsaid liquids through said solution delivery tube comprises at least onesyringe pump.
 27. The apparatus of claim 25, wherein said means formixing said liquids before said liquids exit said solution delivery tubecomprises an external mixer.
 28. The apparatus of claim 25, wherein saidmeans for mixing said liquids before said liquids exit said solutiondelivery tube comprises a frit, said frit embedded in said rod.
 29. Theapparatus of claim 25, wherein said means for controlling the positionof said apparatus over said array comprises robotics.
 30. A system forelectrochemically screening an array of materials, said systemcomprising: an array of materials having an individually addressableelectrode for each material in the array; and means associated with eachof said electrodes for simultaneously testing each of said materials forsaid specific material property.
 31. The system of claim 30, whereinsaid means comprises an electrochemical cell, a multi-channelpotentiostat, and a printed circuit board assembly.
 32. The system ofclaim 31, wherein said electrochemical cell comprises: a cylindricalglass housing, said housing sandwiched between two end members and heldin place with at least four screw fasteners; a reference electrodecompartment; a liquid filling hole; a cathode assembly; and an anodearray assembly, said anode array assembly holding said array ofindividually addressable electrodes.
 33. The system of claim 32, whereinsaid anode array assembly comprises: a first o-ring, said first o-ringforming a water-tight seal with said glass housing; a molded adapterhaving an inner flange, an outer flange, and at least one groove; anarray of individually addressable electrodes; a second o-ring, saidsecond o-ring fitting into said groove and forming a water-tight sealwith said array of individually addressable electrodes; a printedcircuit board; a ring of elastomeric contacts, said elastomeric contactslocated between said array and said printed circuit board; and a backingplate.
 34. The system of claim 33, wherein said printed circuit boardcomprises: a predetermined number of contact pads, said number ofcontact pads corresponding to the number of individually addressableelectrodes on said array; at least four high density pin connectors; acommon reference electrode contact; and a common counter electrodecontact.
 35. A method of testing a specific property of a material, saidmethod including the steps of: depositing distinct materials on an arrayof individually addressable electrodes; placing said array in anelectrochemical cell; and screening said array for said specificproperty.
 36. The method of claim 35, wherein said screening comprises:pulsing all of said electrodes on said array to a predeterminedpotential and monitoring and recording the current that is passed. 37.The method of claim 35, wherein said specific property for said array isscreened in a time frame of less than 5 minutes.